In today's operation of smaller or lighter vehicles in mixed traffic with larger and heavier vehicles it is generally understood that the smaller and lighter vehicles and their occupants carry a higher risk of damage and injury than do the larger and heavier vehicles and their occupants. An extreme illustration occurs where a small sports car is broad sided by a loaded semi-tractor trailer truck at full speed. There is also much concern over disparate contact heights for front and rear impacts. Due to these issues, the buying public has heavily migrated to purchasing larger and safer vehicles (by size and weight, and perceptions from a higher ride height). Yet, today there is critical need for improving the fuel efficiency of vehicle traffic. Significant efficiency gain could come from changing commuters from transporting one or two people (300 lbs.) in larger vehicles (5,000 lbs.), to transporting the same commuters (300 lbs.) in lighter and more aerodynamic vehicles (1,500 lbs, for instance).
However, the realities stated above on the public perceptions of personal safety in mixed traffic and the realities of the trucking industry's continued existence on the roads, all have actually led to a cultural situation seriously limiting acceptance of present fuel efficient vehicles. By simple physics, a larger mass impacting a smaller mass, will impart greater energy into the smaller mass. This results in either: (1) a greater rate of deceleration of the smaller mass as the larger mass is decelerated by the impact, which then accelerates the smaller vehicle in the larger mass' original direction or (2) the smaller mass absorbs the larger energy in the crushing of the vehicle body of the smaller mass. Hence, the slowing of deceleration and absorbing of energy is the lighter vehicle's defense. These are the principles of both the move to larger vehicles for safety and of the move to airbag systems.
Much work has been done in designing a vehicle's ability to absorb frontal and rear impact with large and controlled crush zones. However, in a side impact scenario, today's vehicles position the occupant's body less than 8 inches from the point of impact of a large, high speed vehicle. This leaves little room for either a crush zone or the adequate operation of an airbag system. Lighter three and four wheel vehicle concepts have been advanced, including positioning the vehicle's occupants in tandem and providing greater distance from the side points of the tires to the occupants. However, the designs have not provided any significant advance in crash protection. The vehicles are still highly vulnerable in traffic with large trucks, and even more so perceptually. If a lighter vehicle is to provide equal protection to that of larger vehicles on the road, it must be designed to absorb much greater impact, and the vehicle must readily communicate its safety advantages to the potential buying public in order to achieve acceptance and hence shift drivers to the use of lighter vehicles, thus positively impacting the overall fuel efficiency of the transportation fleet.
Vehicles are available with front guards, known as brush guards or kangaroo guards (in Australia). These guards are for the purpose of keeping animals from coming over the hood of the vehicle in a contact situation and for protecting the vehicle from damage due to contact with brush and small trees during off-road operation. While today most are of cosmetic function only, functional ones are only on larger vehicles and are not for the purpose of occupant crash protection from another vehicle. Rear aerodynamic devices, or spoilers are utilized as external components of vehicles for primarily cosmetic purposes, such as relating a marketing connection to racing. In cases where they are functional, they are designed for aerodynamic purposes only, and do not function as crash protection devices.